Somatosensory evoked potentials: Part II. A review of the clinical applications in pediatric neurology

Somatosensory evoked potentials in clinical practice: a review

The authors present a review of the current use of somatosensory evoked potentials (SSEPs) in neurological practice as a non-invasive neurophysiological technique. For this purpose we have reviewed articles published in English or Portuguese in the PubMed and LILACS databases. In this review, we address the role of SSEPs in neurological diseases that affect the central nervous system and the peripheral nervous system, especially in demyelinating diseases, for monitoring coma, trauma and the functioning of sensory pathways during surgical procedures. The latter, along with new areas of research, has become one of the most important applications of SSEPs.

Utility and practice of electrodiagnostic testing in the pediatric population: An AANEM consensus statement

Nerve conduction studies and needle electromyography, collectively known as electrodiagnostic (EDX) studies, have been available for pediatric patients for decades, but the accessibility of this diagnostic modality and the approach to testing vary significantly depending on the physician and institution. The maturation of molecular diagnostic approaches and other diagnostic technologies such as neuromuscular ultrasound indicate that an analysis of current needs and practices for EDX studies in the pediatric population is warranted. The American Association of Neuromuscular & Electrodiagnostic Medicine convened a consensus panel to perform literature searches, share collective experiences, and develop a consensus statement. The panel found that electrodiagnostic studies continue to have high utility for the diagnosis of numerous childhood neuromuscular disorders, and that standardized approaches along with the use of high-quality reference values are important to maximize the diagnostic yield of these tests in infants, children, and adolescents.

Sulfatide levels correlate with severity of neuropathy in metachromatic leukodystrophy

Objective

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disorder due to deficient activity of arylsulfatase A (ASA) that causes accumulation of sulfatide and lysosulfatide. The disorder is associated with demyelination and axonal loss in the central and peripheral nervous systems. The late infantile form has an early-onset, rapidly progressive course with severe sensorimotor dysfunction. The relationship between the degree of nerve damage and (lyso)sulfatide accumulation is, however, not established.

Methods

In 13 children aged 2–5 years with severe motor impairment, markedly elevated cerebrospinal fluid (CSF) and sural nerve sulfatide and lysosulfatide levels, genotype, ASA mRNA levels, residual ASA, and protein cross-reactive immunological material (CRIM) confirmed the diagnosis. We studied the relationship between (lyso)sulfatide levels and (1) the clinical deficit in gross motor function (GMFM-88), (2) median and peroneal nerve motor and median and sural nerve sensory conduction studies (NCS), (3) median and tibial nerve somatosensory evoked potentials (SSEPs), (4) sural nerve histopathology, and (5) brain MR spectroscopy.

Results

Eleven patients had a sensory-motor demyelinating neuropathy on electrophysiological testing, whereas two patients had normal studies. Sural nerve and CSF (lyso)sulfatide levels strongly correlated with abnormalities in electrophysiological parameters and large myelinated fiber loss in the sural nerve, but there were no associations between (lyso)sulfatide levels and measures of central nervous system (CNS) involvement (GMFM-88 score, SSEP, and MR spectroscopy).

Interpretation

Nerve and CSF sulfatide and lysosulfatide accumulation provides a marker of disease severity in the PNS only; it does not reflect the extent of CNS involvement by the disease process. The magnitude of the biochemical disturbance produces a continuously graded spectrum of impairments in neurophysiological function and sural nerve histopathology.

Correlation between electrophysiological properties, morphological maturation, and olig gene changes during postnatal motor tract development

This study investigated electrophysiological and histological changes as well as alterations of myelin relevant proteins of descending motor tracts in rat pups. Motor-evoked potentials (MEPs) represent descending conducting responses following stimulation of the motor cortex to responses being elicited from the lower extremities. MEP responses were recorded biweekly from postnatal (PN) week 1 to week 9 (adult). MEP latencies in PN week 1 rats averaged 23.7 ms and became shorter during early maturation, stabilizing at 6.6 ms at PN week 4. During maturation, the conduction velocity (CV) increased from 2.8 ± 0.2 at PN week 1 to 35.2 ± 3.1 mm/ms at PN week 8. Histology of the spinal cord and sciatic nerves revealed progressive axonal myelination. Expression of the oligodendrocyte precursor markers PDGFRα and NG2 were downregulated in spinal cords, and myelin-relevant proteins such as GalC, CNP, and MBP increased during maturation. Oligodendrocyte-lineage markers Olig2 and MOG, expressed in myelinated oligodendrocytes, peaked at PN week 3 and were downregulated thereafter. A similar expression pattern was observed in neurofilament M/H subunits that were extensively phosphorylated in adult spinal cords but not in neonatal spinal cords, suggesting an increase in axon diameter and myelin formation. Ultrastructural morphology in the ventrolateral funiculus (VLF) showed axon myelination of the VLF axons (99.3%) at PN week 2, while 44.6% were sheathed at PN week 1. Increased axon diameter and myelin thickness in the VLF and sciatic nerves were highly correlated to the CV (rs > 0.95). This suggests that MEPs could be a predicator of morphological maturity of myelinated axons in descending motor tracts.

Somatosensory evoked potential for detection of subclinical neuropathy in Egyptian children with acute lymphoblastic leukaemia

To evaluate neurological changes developing during paediatric Acute Lymphoblastic Leukaemia (ALL) therapy clinically and through electrophysiological Study of Somatosensory Evoked Potentials (SSEPs) changes in different phases of therapy. Thirty five-ALL patients with age range from 3-14 years were included compared to 30 healthy controls. History, neurological examination, complete blood counts, cytological examination of bone marrow aspirate and cerebrospinal fluid with Measurement of Serum Methotrexate (MTX) were done. The SSEPs were performed and patients subjected to another SSEP with measurement of serum MTX level before and 10 days after intra-thecal injection (IMTX). Clinical neurological findings in patients after induction were depressed deep tendon reflexes (43.3%), hypotonia (28.6%), lost pain sensation (28.6%), muscle weakness (17.1%) and movement disorders (17.1%). Percentage of delayed SSEPs after induction were at levels of brachial plexus (28.6%), spinal cord (68.6%), cortical conduction (31.4%), ERB-N13 Inter Peak Latency (IPL) (74.3%) and N13-N20 IPL (17.1%) in the studied patients. Significant prolonged latency of N13 (p = 0.005), N20 (p = 0.04) and IPL of ERB-N 13 (p = 0.005), N13-N20 (p = 0.01), Inter-Side Difference (ISD) of N13 (p = 0.01), ERB-N13 (p = 0.02) and N13-N20 (p = 0.03) after induction compared to values at diagnosis. Significant positive correlation were found between serum MTX after IMTX with N13-N20 IPL (p = 0.01), N20 ISD (p = 0.03) with significant prolongation in N20 latency, N13-N20 IPL and ISD of N20 compared to values before injection. ALL patients have prolonged latency of SSEPs at cervical cord and cortical levels which increased after IMTX due to axonal injury throughout the cord. SSEPs could be an early diagnostic tool for subclinical neuropathy.

Somatosensory-evoked fields on magnetoencephalography for epilepsy infants younger than 4 years with total intravenous anesthesia

OBJECTIVE

Patients must remain immobile for magnetoencephalography (MEG) and MRI recordings to allow precise localization of brain function for pre-surgical functional mapping. In young children with epilepsy, this is accomplished with recordings during sleep or with anesthesia. This paper demonstrates that MEG can detect, characterize and localize somatosensory-evoked fields (SEF) in infants younger than 4 years of age with or without total intravenous anesthesia (TIVA).

METHODS

We investigated the latency, amplitude, residual error (RE) and location of the N20m of the SEF in 26 infants (mean age=2.6 years). Seventeen patients underwent TIVA and 9 patients were tested while asleep, without TIVA.

RESULTS

MEG detected 44 reliable SEFs (77%) in 52 median nerve stimulations. We found 27 reliable SEFs (79%) with TIVA and 13 reliable SEFs (72%) without TIVA. TIVA effects included longer latencies (p<0.001) and lower RE (p<0.05) compared to those without TIVA. Older patients and larger head circumferences also showed significantly shorter latencies (p<0.01).

CONCLUSIONS

TIVA resulted in reliable SEFs with lower RE and longer latencies.

SIGNIFICANCE

MEG can detect reliable SEFs in infants younger than 4 years old. When infants require TIVA for MEG and MRI acquisition, SEFs can still be reliably observed.

MEG event-related desynchronization and synchronization deficits during basic somatosensory processing in individuals with ADHD

Background

Attention-Deficit/Hyperactivity Disorder (ADHD) is a prevalent, complex disorder which is characterized by symptoms of inattention, hyperactivity, and impulsivity. Convergent evidence from neurobiological studies of ADHD identifies dysfunction in fronto-striatal-cerebellar circuitry as the source of behavioural deficits. Recent studies have shown that regions governing basic sensory processing, such as the somatosensory cortex, show abnormalities in those with ADHD suggesting that these processes may also be compromised.

Methods

We used event-related magnetoencephalography (MEG) to examine patterns of cortical rhythms in the primary (SI) and secondary (SII) somatosensory cortices in response to median nerve stimulation, in 9 adults with ADHD and 10 healthy controls. Stimuli were brief (0.2 ms) non-painful electrical pulses presented to the median nerve in two counterbalanced conditions: unpredictable and predictable stimulus presentation. We measured changes in strength, synchronicity, and frequency of cortical rhythms.

Results

Healthy comparison group showed strong event-related desynchrony and synchrony in SI and SII. By contrast, those with ADHD showed significantly weaker event-related desynchrony and event-related synchrony in the alpha (8–12 Hz) and beta (15–30 Hz) bands, respectively. This was most striking during random presentation of median nerve stimulation. Adults with ADHD showed significantly shorter duration of beta rebound in both SI and SII except for when the onset of the stimulus event could be predicted. In this case, the rhythmicity of SI (but not SII) in the ADHD group did not differ from that of controls.

Conclusion

Our findings suggest that somatosensory processing is altered in individuals with ADHD. MEG constitutes a promising approach to profiling patterns of neural activity during the processing of sensory input (e.g., detection of a tactile stimulus, stimulus predictability) and facilitating our understanding of how basic sensory processing may underlie and/or be influenced by more complex neural networks involved in higher order processing.

Myelopathy due to intrathecal chemotherapy: report of six cases

Intrathecal chemotherapy and systemic chemotherapy are used for both prophylaxis and treatment of central nervous system disease in hematologic malignancies. However, intrathecal treatment has some adverse effects, such as arachnoiditis, progressive myelopathy, and leukoencephalopathy. The authors describe six children in whom myelopathy and adhesive arachnoiditis developed after administration of intrathecal chemotherapy including methotrexate, cytosine arabinoside, and prednisolone. Urinary retention and incontinence, the main presenting complaints in all patients, developed within 12 hours after intrathecal therapy and spontaneously resolved within 7 days. Two patients were unable to walk. In these two, weakness in the lower extremities gradually recovered by 1 month but urinary incontinence did not improve. None of the children had sensory loss. On follow-up periodic recurrent urinary tract infection was noted in four patients. MRI findings corresponded to arachnoiditis. No response was recorded on tibial nerve somatosensory evoked potentials in all patients. Intrathecal chemotherapy, especially methotrexate, can cause spinal cord dysfunction in children with acute lymphoblastic leukemia and non-Hodgkin's lymphoma. Arachnoiditis should be kept in mind as a causative factor in recurrent urinary tract infection in patients receiving intrathecal chemotherapy.

Chemotherapy for acute lymphoblastic leukemia may cause subtle changes of the spinal cord detectable by somatosensory evoked potentials

Intrathecal chemotherapy has been determined to cause transient or permanent paraparesis due to myelopathy in patients with leukemia or other malignancies. To systematically evaluate the effect of methotrexate on spinal cord function, somatosensory evoked potentials (SEP) were measured in children with acute lymphoblastic leukemia (ALL). A prospective evaluation was performed in 38 consecutive children aged 1.4-15.3 years with newly diagnosed ALL during treatment. Intrathecal methotrexate therapy was included in the therapy schedule of all patients as central nervous system (CNS) therapy in addition to intravenous chemotherapy in 19 standard risk patients and intravenous chemotherapy with cranial irradiation in 19 intermediate or high-risk patients. The measured conduction times were compared with those of 38 control children matched for age, height, and sex. A significant increase in the conduction time of the tibial nerve SEP was found between the Th12 level and the cortex in children with ALL after receiving intrathecal methotrexate therapy during the induction and CNS therapy phases when compared with their controls. The difference of the mean latencies was 1.45 ms (95% CI 0.39-2.51; P < 0.01). There was no significant delay in the median nerve SEP from the brain stem to the cortex, indicating that the conduction delay was in the area of the spinal cord exposed to intrathecal methotrexate. Moreover, the cortical amplitudes of the median nerve SEPs were significantly reduced when measured immediately after intravenous and intrathecal methotrexate and compared to the amplitudes measured after induction therapy in standard risk patients (P = 0.001). Intrathecal methotrexate with systemic chemotherapy causes a deterioration in the somatosensory pathways within the CNS, suggesting also spinal cord dysfunction in children with ALL in addition to the cerebral dysfunction described earlier.

Treatment of obstructive sleep apnea in achondroplasia: evaluation of sleep, breathing, and somatosensory-evoked potentials

The occurrence of obstructive sleep apnea (OSA) is achondroplasia has been linked to brain stem compression. Overnight sleep studies (11 subjects) and somatosensory-evoked potentials (SEP's, 10 subjects) were recorded before and after conventional treatment of OSA in achondroplasia. The two groups were derived from 30 subjects who underwent diagnostic sleep studies and SEPs, including 15 females and 15 males with a median age 6.6 years (range 1.0-47.6) at the time of the first study. In 30 initial studies there was no correlation between severity of OSA and abnormalities on SEP evaluation. Treatment of 17 subjects included adenotonsillectomy (n = 3), weight loss (n = 1), and nasal-mask continuous positive airway pressure (CPAP) (n = 13). Sleep studies in 11 subjects after a delay of 8.8 +/- 2.8 months showed a reduction in respiratory disturbance index (RDI) from 38.4 +/- 6.9 to 6.5 +/- 1.8 events hr(-1) (p < 0.001) and movements/arousals fell from 10.4 +/- 2.2 to 4.8 +/- 0.2 hr(-1) (p < 0.04). Obstructive events were reduced from 33.7 +/- 6.9 to 2.4 +/- 1.0 hr(-1) (p < 0.001). Improvement of respiratory indices was associated with an increased proportion of slow-wave sleep from 25.2 +/- 4.0% to 32.3 +/- 2.4% (p = 0.01), and decrease in stage 1-2 sleep from 59.3 +/- 5.8% to 46.6 +/- 1.9% (p = 0.03). There was no increase in the percentage of REM sleep (15.2 to 21.2%). Repeat SEP studies in 10 subjects, after clinically effective treatment of OSA, showed improvement of SEP score of at least 1 grade, in 5 of 7 (71%) with initially abnormal values. We conclude that treatment of relieve upper airway obstruction improves OSA in achondroplasia, accompanied by changes in sleep structure and, in some cases, improved studies of neurological function.

Vincristine therapy for children with acute lymphoblastic leukemia impairs conduction in the entire peripheral nerve

Somatosensory evoked potentials were measured prospectively in 38 children with acute lymphoblastic leukemia to evaluate the side effects of vincristine therapy on conduction of the peripheral nerves. Nineteen patients at standard risk received vincristine 12 mg/m2 during induction therapy and 19 patients at intermediate or high risk received 6 mg/m2 during induction therapy and an additional 6 mg/m2 during delayed intensification therapy. These latencies were compared with those of 38 age-, height-, and sex-matched controls. A prolongation in the peripheral conduction time of the posterior tibial nerve was found in the standard risk patients after induction compared with that of the controls, and a delay was found not only from the ankle to the popliteal fossa, but also from the popliteal fossa to the spinal cord (P < .01). The conduction times of the median nerve from the wrist to the plexus (P < .01) and from the wrist to the spinal cord (P < .01) were prolonged after delayed intensification therapy. There was a significant delay in the median and tibial nerve conduction between the intermediate and high risk patients and their controls after a total vincristine dose of 12 mg/m2. These delays were found along the entire length of the nerves, especially in the proximal part of the tibial nerve (P < .001).

Evoked potentials in children with chronic renal failure, treated conservatively or by continuous ambulatory peritoneal dialysis

Children with chronic renal failure (CRF) show developmental, intellectual and motor disturbances. It is questionable if an early start of renal replacement therapy may prevent or delay these disturbances. We studied the neurological and intellectual development of children < 5 years suffering from CRF (creatinine clearance < 20% of normal) prospectively, over a period of 3 years. As part of the neurological study, brainstem auditory evoked potentials (BAEP) and somatosensory evoked potentials (SSEP) were recorded. Measurements were performed in a group of 22 children every 6 months. In 18 of these children CRF was present from birth. Sufficient data were available for analysis in 19 (BAEP) and 22 (SSEP), respectively. A delay of peak I of BAEP gave indications for peripheral conduction disturbances, possibly due to cochlear dysfunction. Brainstem conduction was normal. There were no differences between the children treated conservatively (n = 9) and those treated with continuous ambulatory peritoneal dialysis (CAPD) (n = 10). In children < 2.5 years SSEP showed a delayed thalamocortical conduction, which was not observed in older children. This might indicate a delayed myelination in young children with CRF. No differences were found between the children treated conservatively (n = 10) and those treated with CAPD (n = 12).

Evoked potentials in children with oxidative metabolic defects leading to Leigh syndrome

We studied evoked potentials in 15 children (age range: 2 wks to 4 yrs; mean: 10 mos) with metabolic disturbances that led to Leigh syndrome. These disturbances included deficiencies of pyruvate dehydrogenase (N = 5), complex 1 (N = 7), complex 4 or cytochrome oxidase (N = 2), and complex 5 (N = 1) deficiencies. Subsequent studies were performed in 11 children. All of the children with pyruvate dehydrogenase deficiency had abnormal brainstem auditory evoked potentials (BAEPs) due to poor morphology and reproducibility of the waveforms; central conduction time was normal in 4 of 5 initial studies. The patients with complex 4 or cytochrome oxidase deficiency had abnormal BAEPs, due to increased interpeak latencies and low amplitude or absent waves IV/V. Six of 7 of the children with complex 1 deficiency had normal BAEPs. The remaining patient (the youngest, age 6 wks) had only waves I and II bilaterally and suffered from the rapidly progressive form of complex 1 deficiency; the other 6 with complex 1 deficiency had the slowly progressive form. The one patient with complex 5 deficiency had normal BAEPs when first tested at 4 mos; abnormal BAEPs with loss of later waves were observed 10 weeks later. The visual evoked potentials and somatosensory evoked potentials usually were abnormal in these patients, but the findings were not specific to the patient subgroups. In all but one patient, subsequent studies disclosed a lack of normal maturational changes and/or deterioration across all 3 modalities. The BAEPs appeared to covary with the specific metabolic findings in these patients and with the patient's clinical course, but no BAEP could be considered characteristic of Leigh syndrome.

The use of somatosensory evoked potentials in infants and children

Somatosensory evoked potentials (SSEPs) are a useful, reliable means of assessing function of the somatosensory system. Complex maturational changes of the CNS such as synaptogenesis and myelination, as well as body growth, complicate interpretation of SSEPs. An understanding of these factors enhances clinical interpretation in infants and children.

Continuous electrophysiologic monitoring of cerebral function in the pediatric intensive care unit

The brains of children admitted to intensive care units are at considerable risk. Electrophysiologic techniques are the most suitable of available methods for uninterrupted surveillance of brain function. Although the use of routine electroencephalography for this purpose is impractical, automated electroencephalographic signal analysis and application of digital computer technology have made continuous monitoring of cerebral function feasible. Various methods of displaying modified electroencephalographic data in an understandable and interpretable form have been developed; the most commonly used devices are the cerebral function monitor and the compressed spectral array. Practical clinical applications and limitations of continuous cerebral function monitoring are discussed.